This invention relates to an improvement in abrading tools and, in particular, to wheel or disk type abrading tools and most particularly to rigid diamond or cubic boron nitride grinding wheels of increased efficiency and lower cost.
The grinding wheel art is highly developed and of long standing as is evidenced by standard texts such as The Grinding Wheel, A Textbook of Modern Grinding Practice by Kenneth B. Lewis, published by The Judson Company, Cleveland, Ohio, 1951, revised edition 1959, under the auspices of the Grinding Wheel Institute. The art of grinding, to which the present invention pertains, including its history, prior development, and the practice current at that time, is described in Chapter 19 of the Lewis work, supra.
In the past, as described by T. Pohl et al, U.S. Reissue Pat. No. 19,802 issued Dec. 31, 1935, abrading materials were interspersed in a matrix containing substantial amounts of preferably uniformly formed cells or holes separated from each other by walls of the abrading mixture; i.e., the abrading material was distributed throughout a porous matrix. The cells or holes could be of various shapes such as ball-like, cylindrical or other, and the size could vary over a wide range. The form and size of the cells was controlled to a considerable extent by the particular abrading material used, the binding material, and by the type of work to which the grinding tool was to be subjected.
The optimum size and form of the cells and their relation to the size of the abrading material was determined by empirical testing. The Pohl patent specifically describes a grinding disk having a honeycomb formation in which hollow cells are uniformly distributed throughout the entire disk, the cells being surrounded by comparatively thin wall of the selected matrix and abrading material. The cells extended from the periphery of the disk to the axis, and each cell was generally cylindrical or ball-shaped. Such abrading disks were said to have many advantages over previous grinding disks, since as the abrading particles and matrix of the cellular structure wore away, new hollow cells continuously opened to expose fresh cutting edges. Inasmuch as the hollow spaces or cells were substantially large as compared to the particles moved from the material being ground, the cells were not clogged dby this extraneous matter, thus providing what is known in the art as swarf relief.
Similarly, Smith et al U.S. Pat. No. 3,495,359, issued Feb. 17, 1970 describes a core drill structure having a perforate supporting body with diamond abrasive adhered to all surfaces of the working portion intermediate the perforations in the body. This reference described prior diamond impregnated tools in which a mixture of bond and diamond grits was molded to the desired shape before the bond was set. It was noted that various types of ceramic and resin bonds had been used for this purpose, but that it had been preferred to use particulate metal alloy bond components, i.e. powder metalurgy type for the most difficult cutting operations. Smith et al also noted that various designs had been provided to permit free circulation of flushing fluids to wash away the swarf in such drilling operations. It was said that such swarf relief was essential to cool the tool and clear the debris in front of the tool so that the diamond particles in the exposed end of the tool could be pressed against the material being cut. Smith et al specifically described tools in which a cylindrical core member, as the working portion of the core drill, was formed of a sheet of woven metal design, or a tubular seamless wire mesh braid. The perforations in the member or holes in the woven screen and braid were arranged in a pattern so that in any plane the apertures overlapped one another. By placing the diamond grits on all surfaces of the sides of the working end of the braid, screen or perforated member, a substantially three-dimensional distribution of diamond particles was obtained so that as the tool wore in use, new diamond particles were exposed.
While the foregoing disclosures were significant advances in the art, it has long been apparent that further improvements were needed to increase the efficiency and lower the cost of production and operation of such grinding tools.